Most homes and commercial buildings utilize electrical wiring systems to distribute power throughout the structure. Typically, electrical wiring systems carry a 120 or 240 volt signal at 15 or 30 amps, respectively, to provide electrical power for lighting systems, climate control systems, appliances, and other electrical loads. Many accidents occur annually due to penetrations of electrical wires or due to deterioration of older wiring systems.
According to reports issued by the Consumer Products Safety Commission (CPSC) in 1997, home wire systems caused over 40,000 fires that resulted in 250 deaths and over $670 million of property damage. Further study by the CPSC based on 40,300 electrical circuit fires showed that 36% were due to installed wiring and 16% were due to cord/plugs.
Today, circuit breakers primarily protect against certain overload and short circuit conditions which occur primarily in fixed wiring. The overload protection is provided by the slow heating of a bimetal strip that breaks the circuit causing the breaker to trip after a specified period of time. Additionally, the lower limit of the magnetic trip setting may be determined by the manufacturer such that the device does not nuisance trip on high inrush loads. Accordingly, in order to avoid false trips, the tripping of a circuit breaker based on a wide variety of wire faults present on a connected electrical wire may be a relatively slow event. This relatively slow tripping may lead to property damage and/or personal injury.
Circuit breakers do not protect against all hazards that may occur within electrical wiring systems. For example, circuit breakers are not effective in detecting arc faults. Therefore, in addition to circuit breakers, there are many other safety devices that have been designed for use with electrical wiring. One such safety device that is commonly installed in electrical wiring systems is a Ground Fault Circuit Interrupter (GFCI). A GFCI measures the difference between the currents flowing through the hot conductor and the neutral conductor of a conventional electrical wire. If the difference between the current flowing through the hot conductor and the current flowing through the neutral conductor exceeds a few milliamps, the presumption is that current is leaking to ground via some other path. This may be because of a short circuit to, for example, the chassis of an appliance, or to the ground lead, or through a person. Any of these situations may be hazardous, so the GFCI trips, breaking the circuit. However, similar to circuit breakers, a GFCI may be a relatively slow device in order to avoid false tripping. Additionally, a GFCI is often not effective at detecting certain types of wire faults, such as arc faults.
Another safety device that is commonly installed in electrical wiring systems is an Arc Fault Circuit Interrupter (AFCI). An AFCI adds electronic protection to the standard thermal and magnetic protection provided by circuit breakers. The circuitry in an AFCI detects specific arcs that are determined to be likely to cause a fire. The AFCI uses electronics to recognize the current and voltage characteristics of the arcing faults on the electrical wire, and interrupts the circuit when a fault is detected. Each AFCI has circuit logic, and perhaps control logic, that is designed to detect specific types of arc faults. These arc faults are specific to the type of wiring the AFCI is designed to be implemented with. Additionally, in order to avoid false tripping, an AFCI circuit is typically required to analyze an electrical signature for a relatively long period of time. These delays may be hazardous, leading to property damage and/or personal injury.
Another problem with many electrical wire safety devices is that they require manual intervention and/or manual reset once a fault is detected. The electrical wire safety devices are not capable of making a determination of when a fault is no longer present on a monitored wire and, therefore, will maintain the wire in a de-energized state. This inability to determine when a fault is no longer present can lead to undesirable situations. For example, an electrical wire that provides power to a refrigerator or freezer may be de-energized by an electrical wire safety device and, if a user does not reset the safety device, perishable food items may spoil.
Accordingly, improved safety devices capable of rapidly detecting wire faults and/or other relatively dangerous conditions are desirable.